。
She's old enough to have more sense.
Literal
[topic-は] more discretion [subject-が] exist-and good age [explanatory-だ].
分別 (ふんべつ, not ぶんべつ — note the reading) means 'discretion, good judgment, common sense' — the kind of wisdom that comes with maturity. The same kanji read ぶんべつ means 'classification, sorting' (as in ゴミの分別 'trash sorting'), so reading is critical. 分別があってよい年配 literally 'an age that ought to have discretion' uses the te-form あって as a connecting clause and よい ('good') to mean 'fitting, appropriate.' The whole sentence says 'she's at an age where she should know better.'